Although there is no single cause for multiple sclerosis, one priority in research is to identify different risk factors associated with MS. A risk factor is anything that can affect your chances of getting a disease like MS. Some risk factors, like your age, sex, or family history, cannot be changed, and are referred to as non-modifiable risk factors. Others, such as lifestyle and environmental influences, are avoidable and are termed modifiable risk factors, although in some cases changing these factors is easier said than done.
Having one or more risk factors for a disease does not necessarily guarantee that you will develop that disease, but it can increase your chances. On the other hand, some people can have all of the risk factors for a disease and remain disease-free. Take smoking, for example. Although smoking is the number one risk factor for lung cancer, some people can smoke their entire lives without getting lung cancer. Information about risk factors comes from the study of large groups of people, and various risk factors can interact in complex ways; for that reason, making definitive conclusions about how risk factors can lead to disease in each individual person can be tricky. At the end of the day, however, the best way to minimize your chances of developing MS is to manage the risk factors that you can control.
Research on risk factors for MS is constantly evolving, and each new epidemiological study gives us increased insight into ways that we can prevent or minimize the chances of developing MS. Below is a list of some of the known non-modifiable and modifiable risk factors for MS.
Non-modifiable risk factors
Relapsing-remitting MS is approximately three times as common in women as it is in men, although men have a tendency for later disease onset with worse prognosis.
Although MS can occur in most ethnic groups, people of Caucasian descent have an increased susceptibility to MS.
MS is more common in family members of people living with MS, especially among first-degree relatives such as children and siblings. The risk of MS is even higher among identical twins, approximately one in four. However, the risk is not 100% despite the fact that identical twins share all of the same genes, suggesting that there is a complex interaction between our genes and environmental triggers on the development of MS.
Modifiable risk factors
There is strong evidence to suggest that smoking cigarettes is a risk factor for MS. Some evidence also supports a dose-dependent effect of smoking, meaning that smoking more cigarettes can amplify the risk of developing MS. Smoking is also associated with a greater chance of converting from relapsing-remitting MS to secondary progressive disease and a more rapid build-up of disability.
Generally speaking, MS is more common in populations at higher latitudes (further from the equator), although this relationship is not clear-cut, since rates of MS can be extremely low in some ethnic populations living at high latitudes. This suggests that MS may be triggered in some genetically-susceptible individuals by various environmental factors.
Both reduced levels of vitamin D in the blood and low vitamin D intake have been associated with an increased risk of developing MS. Vitamin D is thought to be partly responsible for the latitude effect of MS risk; ultraviolet B (UVB) radiation from sunlight is the primary source of vitamin D synthesis in the skin, and the lower intensity of UVB radiation in the winter months has been linked to vitamin D deficiency during part of the year.
While infection with Epstein-Barr virus (EBV), a type of herpes virus, during childhood can often be without symptoms, infection later in life can lead to a condition called infectious mononucleosis. Population studies have shown that a past history of infectious mononucleosis caused by EBV infection is associated with an increased risk of MS. Most people get infected with EBV at some point in their lives; because of this, EBV on its own does not lead to MS, but it may be necessary for MS to develop.
Preliminary evidence (which I discuss in my recent blog post) suggests that consumption of coffee can act as a protective factor and decrease the risk of developing MS. More details about this relationship will be available in April when the results of the study are presented.
Franklin GM & Nelson L. (2003) Environmental risk factors in multiple sclerosis: Causes, triggers, and patient autonomy. Neurology. 61:1032-34
O’Gorman C et al. (2012) Environmental risk factors for multiple sclerosis: A review with a focus on molecular mechanisms. Int J Mol Sci. 13:11718-52
Sadovnick AD et al. (1996) Evidence for genetic basis of multiple sclerosis. The Canadian Collaborative Study Group. Lancet. 347:1728-30
Wingerchuck DM. (2011) Environmental factors in multiple sclerosis: Epstein-Barr virus, Vitamin D, and cigarette smoking. Mt Sinai J Med. 78(2):221-30
Wingerchuck DM. (2012) Smoking: effects on multiple sclerosis susceptibility and disease progression. Ther Adv Neurol Disord. 5(1):13-22
Image credits: © Cornelius20 | Dreamstime.com – Brain Maze Photo